Apparently dojo has issues with their localization modules that makes it impossible to determine the correct culture info when you have two languages from the same locale registered at the same time.

For example if your editors are from let's say New Zealand the because of this dojo bug https://bugs.dojotoolkit.org/ticket/17155 the language formatting would always fallback to the _ROOT_ nls for them (which is "en" in this case).

It's a very annoying issue as for example number and datetime formatting are different for English editors from US and from GB/NZ/AU.

One could try to solve it by changing the globalization of the whole site or by turning languages in admin mode on and off but in fact the Edit Mode is the only place where we need the change to be visible in.

If you add this simple initializable module to your site it would just affect dojo i18n module without touching the asp.net runtime.